Sensing characteristics based on Fano resonance in rectangular ring waveguide

Sensing characteristics based on Fano resonance in a rectangular ring resonator with a stub are investigated numerically. Simulation results show that a sharp and asymmetric Fano-line shape emerges in the proposed structure. Through tuning the width and length of the stub, it is found that the width and length play an important role in optimizing the sensing characteristic. Using the sharp and asymmetric Fano-line shape a highly sensitive plasmonic nanosensor with the sensitivity of 1000 nm/RIU and a tunable figure of merit (FOM) can be attained. The maximum FOM can reach up to 992,800 when the stub length d=120 nm, width l=130 nm and the refractive index difference Δn=0.05, which is larger than that in previous reports. In addition, the results show that a larger FOM can be obtained by tuning the stub width than tuning its length. The proposed model and results provide guidance for fundamental research of the plasmonic nanosensor applications and designs.